Subsurface Drainage Design Research Articles

Assessing the Performance of Wasim and Drainmod Models for Subsurface Drainage Design and Analysis in a Data-Scarce Environment

Assessing the Performance of Wasim and Drainmod Models for Subsurface Drainage Design and Analysis in a Data-Scarce Environment

Effects of Drainage System Design on Nutrient Leaching and Crop Yield

Highlights Tested drainage system designs had no clear effect on the total amount of drainage discharge. Tested drainage system designs had a clear effect on nutrient loads in drainage discharge. Corrugated plastic pipe drainage systems had higher N loads and lower P loads than tile drainage systems. Corrugated plastic pipe drainage systems gave higher yields than tile drainage systems and can be a profitable on-farm investment. Abstract. A clear strategy for adapting agricultural drainage to future climate change is important for environmental and economic reasons. In a study aimed at developing recommendations for the subsurface drainage design in clay soils, we evaluated the impact of replacing an old drainage system (1920) with new systems (2018) on nutrient leaching and crop yield. Our field experiment included 12 individually drained plots divided into four treatments: (A) old system with clay tiles at 10 m spacing, without an envelope; (B) new system with plastic pipes at 10 m spacing, gravel envelope; (C) new system with plastic pipes at 5 m spacing, gravel envelope; and (D) new system with plastic pipes at 10 m spacing, gravel envelope and lime incorporated in trench backfill. We conducted flow measurement and flow-proportional, logger-controlled water sampling of the drainage discharge from each plot at a measuring station. Preliminary results (first two years) show a clear effect of the new drainage systems on phosphorus and nitrogen loads in drainage discharge. The lowest total load of phosphorus and highest total load of nitrogen in all treatments were observed in treatment D (with 10 m drain spacing and lime incorporated in trench backfill). The highest total phosphorus load and lowest total nitrogen load in all treatments were observed for the old tile drainage system with 10 m drain spacing (treatment A). The environmental impact of new drainage systems on clay soils may thus be a trade-off between decreased phosphorus loads and increased nitrogen loads with more intensive drainage. Crop data from two experimental years indicated that investing in new drainage systems can be profitable for farmers, as crop yield was 3%-20% higher with new drainage systems compared with old tile drainage. More experimental years are needed to determine the long-term effects of the different drainage system designs. Keywords: Drain envelope, Drain spacing, Nitrogen load, Phosphorus load, Subsurface drainage.

Comparative Sensitivity Analysis of Hydrology and Relative Corn Yield under Different Subsurface Drainage Design Using DRAINMOD

DRAINMOD is a process-based hydrologic model used to analyze the effectiveness of various drainage systems and management strategies. In this study, a sensitivity analysis of DRAINMOD hydrologic parameters for two different field settings located at Champaign, Illinois, was performed to determine the most sensitive parameters that affect the subsurface flow and relative productivity of corn. Latin-Hypercube One-Factor-at-a-Time (LH-OAT) was used to determine the sensitivity index of 17 parameters for six objective functions for daily flow, water balance, and relative yield for the productivity of corn. The results indicated that flow and yield were highly sensitive to drainage design parameters such as drainage depth and spacing. Winter flow and the water balance were sensitive to soil thermal conductivity parameters; however, they had no impact on the relative corn yield. The significant difference in sensitivity of the two fields was observed in the hydraulic conductivity of soil layers due to varying thicknesses for different soil types. This study highlights the need for more careful calibration of these sensitive parameters to reduce equifinality and model output uncertainty and appropriate drainage design for optimizing crop productivity and drainage outflow.

Knitted-sock geotextile envelopes increase drain inflow in subsurface drainage systems

A knitted-sock geotextile envelope is commonly used in the USA, Canada, and parts of Europe to prevent sediment entry into agricultural subsurface drain pipes. Sand-slot pipes have a narrow width to prevent sediment from moving into the drain pipe, and they are used in the USA and Canada as a cheaper alternative to knitted-sock-wrapped pipes. The type of drain pipe (sand-slot or sock-wrapped) is important in subsurface drainage design because it affects the entrance head loss caused by the convergence of flowlines toward the drain perforations, thereby influencing the effective radius of the pipe, which in turn affects drain inflow. Although the theoretical effective radius of a knitted-sock-wrapped pipe can be estimated based on analytical equations, no study has experimentally measured it to verify the theoretical equations. This study had two objectives: (1) Experimentally measure the effective radius of sock-wrapped and sand-slot pipes to verify the theoretical method, and (2) comparatively evaluate the drain inflow performance of a sock-wrapped pipe and a sand-slot pipe. We tested the pipe materials in a sand-tank experiment equipped with manometers. The results showed that the measured and theoretical effective radii were 5.5 and 5.6 cm for the sock-wrapped pipe, 0.7 and 0.7 cm for the 4-row sand-slot pipe, and 1.6 and 1.6 cm for the 8-row sand-slot pipe, respectively. This agreement confirmed that the theoretical method reliably estimated the effective radius of the pipes. The sock-wrapped pipe had a considerably lower entrance head loss (0.4 cm) than the 8-row (6.1 cm) and 4-row (10.4 cm) sand-slot pipes, thereby increasing the effective radius of the sock-wrapped pipe. The estimated drain inflow of the sock-wrapped pipe was 12% and 20% higher than that of the 8-row and 4-row sand-slot pipes, respectively. In conclusion, we verified that the theoretical method accurately estimated the effective radius of the pipes and demonstrated that the sock-wrapped pipe had considerably higher drain inflow than the sand-slot pipe.

WaSim model for subsurface drainage design using soil hydraulic parameters estimated by pedotransfer functions

The agricultural drainage engineering community is steadily shifting the design of subsurface drainage systems from the experience-based design approach to the simulation-based design approach. As with any design problem, two challenges are faced; firstly, how to determine all the input data required by the simulation model, and secondly to, a priori, anticipate what the performance of the designed system will be. This study sought to evaluate the performance of the WaSim model to simulate fluctuating water table depths (WTD), and drainage discharges (DD) in KwaZulu-Natal Province, South Africa. Saturated hydraulic conductivity (Ksat), which is an input to the WaSim model, was estimated by the Rosetta computer program, based on soil particle size distribution data, bulk density, and soil water retention characteristics at pressure heads of – 33 and – 1500 kPa. performance of the WaSim model was statistically assessed using the coefficient of determination (R2), coefficient of residual mass (CRM), mean absolute error (MAE), mean percent error (MPE), and the nash–sutcliffe efficiency (NSE). during the validation period, the WaSim model predicted WTDs with R2, CRM, MAE, MPE, and NSE of 0.86, 0.003, 4.9 cm, 6.0%, and 0.98, respectively. In the same validation period, the model predicted DDs with R2, CRM, MAE, MPE, and NSE of 0.57, 0.002, 0.30 mm day−1,11%, and 0.76, respectively. These results suggest that the use of Rosetta-estimated Ksat data as inputs to the WaSim model compromised its accuracy and applicability as a subsurface drainage design tool. Owing to the relatively low R2 value of 0.57, and that the WaSim model was empirically developed, we recommend further improvement on the calibration of the model for it to be suitable for application under the prevailing conditions. Also, in the absence of other means of determining Ksat, we caution the use of Rosetta-estimated Ksat data as inputs to the WaSim model for the design and analysis of subsurface drainage systems in KwaZulu-Natal Province, South Africa.

Predicting the effect of drain depth on profitability and hydrology of subsurface drainage systems across the eastern USA

The choice of drain depth in subsurface drainage design affects system performance. Previous studies have focused on investigating the hydrology of shallow drains at discrete locations. However, to our knowledge, no study has investigated the profitability of shallow drains across a wide range of soil and climatic conditions. The main objective of this study was to comparatively evaluate the effects of 75-cm shallow drains versus 125-cm deep drains on profitability and hydrology of subsurface drainage systems across the eastern USA. We conducted DRAINMOD simulations under continuous corn production (Zea mays L.) using 30 years of weather data (1990–2019) for combinations of three factors: two drain depths, four soils, and seven locations. Simulations were optimized for crop production that maximized annual economic return on investment. The results showed that corn yield for shallow drains went from 1.6% increase to –1.3% decrease with increasing growing-season rainfall from northeast to southeast USA. Shallow drains provided the benefit of reduced year-to-year corn yield variability across the region. Corn yield for coarse-textured soil benefited more from shallow drains than fine-textured soil across the region. Even though shallow drains increased annual benefit from higher corn yield under certain soil and weather conditions, they were less profitable than deep drains (lower benefit-cost ratio and higher payback period). The benefit of drainage discharge reduction under shallow drains generally intensified with increasing annual precipitation from northeast to southeast USA. Results were used to develop an empirical equation for estimating the benefit of drainage discharge reduction with shallow drains in the eastern USA. In conclusion, even though shallow drains were less profitable than deep drains, they provide benefits that may be of interest to farmers and policymakers.

The Study of Subsurface Land Drainage Optimal Design Model

This paper focused on choosing the best design of subsurface land drainage systems in semiarid areas. The study presented three different soil layers with different hydraulic conductivity and permeability, all layers are below the drain level, and the permeability is increasing with depth. A mathematical model was formulated for the horizontal and vertical drainage optimal design. The result was a nonlinear optimization problem with nonlinear constraints, which required numerical methods for its solution. The purpose of the mathematical model is to find the best values of pipes and tubewells spacing, groundwater table drawdown, and pumps operating hours which leads to a minimum total cost of the subsurface drainage design. A computer code was developed in MATLAB environment and applied to the case study. Results show that the vertical drainage was economically better for the case study drainage network design. And the main factor affecting the mathematical model for both pipe and well drainage was the distance between pipes and tubewells. In addition, considering the lifespan of vertical drainage project, the optimal design involves the minimum possible duration of pumping stations. It is hoped that the proposed optimal mathematical model will present a design methodology by which the costs of all alternative designs can be compared so that the least-cost design is selected.

Infiltration into Frozen Silty Clay Loam Soil with Different Soil Water Contents in the Red River of the North Basin in the USA

Predicting surface runoff and flooding in seasonally frozen areas such as the Red River of the North Basin (RRB) in USA is a challenging task. It depends on the knowledge of the complex process of infiltration in frozen soil, such as phase changes of water, ice content and distribution in the infiltration zone (the top 0–30 cm of the soil profile), soil pore size distribution, soil temperature and freeze–thaw cycles. In this study, the infiltration rates into frozen soil (Colvin silty clay loam according to the United States Department of Agriculture (USDA) Classification, and Chernozem according to Food and Agriculture Organization of the United Nations (FAO) international soil Classification) were measured at three different initial water contents: permanent wilting point (PWP), θpwp; field capacity (FC), θfc; and between FC and PWP, θmid. Laboratory infiltration experiments were conducted using a Cornell sprinkle infiltrometer with three replications for each initial water content. Volumetric soil water content (θv) and soil temperature at three depths were also continuously monitored using sensors. The average infiltration rates were 0.66, 0.38, and 0.59 cm/min for three initial water contents (θpwp, θmid, and θfc, respectively). Initial infiltration into frozen soil occurred quickly in the soil with θpwp because the soil was dry. Melted ice water contributed to the total soil water content over time, so it made the initial infiltration comparatively slower in the soil with θmid. Initial infiltration was also slower in the soil with θfc because the wet soil had very small pore space, so the soil rapidly reached its saturation after the infiltration started. The Horton infiltration equation was fitted with the observed infiltration rates for the soils with three initial water contents, and the goodness of fit was evaluated by using the coefficient of determination (R2) and the root-mean-square error (RMSE). The final infiltration rates from the fitted Horton equations were 0.060, 0.010, and 0.027 cm/min for the initial water contents (θpwp, θmid, and θfc, respectively). The soil water content along the soil profile changed with the amount of infiltrating water over time. However, the initial soil water content and melt water from ice resulting from soil temperature rise regulated the change in soil water content. The amount of ice melt water contribution to soil water content change varied among the soils with different initial water contents (θpwp, θmid, and θfc, respectively). The θv changed gradually in the θpwp soil, rapidly at 0 °C in the θmid soil, and less in the θfc soil. The change in pore distribution due to freeze–thaw cycles and soil packing altered the soil hydraulic properties and the infiltration into the soil. This study can provide critical information for flood forecasting model and subsurface drainage design in the RRB.

Drainmod-Linked Interface for Evaluating Drainage System Response to Climate Scenarios

Abstract.This article presents the development of a drainage-climate interface that incorporates climatological data, crop drainage requirements, and drainage theory into a procedure for characterizing drainage system response under different climate scenarios. The drainage-climate interface is suitable for assessing potential county-level impacts of climate change on crop production, soil hydrology and subsequently on subsurface drainage design. Climate model projections from two general circulation models (GCMs), namely CCSM4 (Community Climate System Model) and MIROC5 (Model for Interdisciplinary Research on Climate), were used to create the climatological database for the drainage-climate interface. DRAINMOD was integrated into the Visual Basic for Applications (VBA) portion of the interface to simulate the performance of subsurface drainage systems in Illinois for the near future (2040 to 2069) and the far future (2070 to 2099) periods. Case studies were developed with the interface for Adams and Champaign Counties in Illinois for their predominant soil types. Hydrologic simulations from the interface were used to determine the optimal depth and spacing of tile drains that maximize crop yield for corn and soybean during the mid and late 21st century. Drainage water management (DWM) was incorporated into the drainage-climate interface to investigate the potential of DWM in the future climate scenarios to maintain water quality, reduce nutrient losses and minimize pollutant loading from drained fields by controlling the timing and amount of water discharged from agricultural drainage systems. Results from DRAINMOD simulations with MIROC5 show a significant decline in crop yield due to extreme heat stress. Corn yield in the future showed a severe reduction while the yield for soybean demonstrated a gradual decline over the years. DWM had only a minimal effect on future crop yield trends. The drainage-climate interface simulated subsurface drainage conditions and made evident the consequences of environmental conditions on crop physiological processes under scenarios of climate change predicted by MIROC5. Keywords: Agricultural system models, Climate change impacts, Drainage-climate interface, Drainage water management, Subsurface drainage, Tile drain depth, Tile drain spacing.

Evaluating Effect of Subsurface Drain Spacing and Depth on Hydrological Properties of Waterlogged Vertisols in Sangli, Maharashtra

A field experiment was conducted to evaluate the effect of subsurface drain spacing and depth on hydrological properties of waterlogged Vertisols under sugarcane in Sangli district of Maharashtra during 2012-13 to 2013-14. A total of 12 treatments consisting four drain spacings of 10, 20, 30 and 40 m and three drain depths of 0.75, 1.0 and 1.25 m were laid in experimental plot. The saturated hydraulic conductivity of soil was determined before and after harvesting of sugarcane. Drainable porosity of soil corresponding to water table depth was determined from water table drawdown and drain discharge measurements after rainfall. It was found that the closely-spaced and deep drain recorded better hydrological properties of soil (drainage coefficient, water table depth, saturated hydraulic conductivity, and drainable porosity) as compared to widely-spaced and deep drains. But closely-spaced drains increased the initial adoption cost of subsurface drainage system, drained excess water, and leached more nutrients. Drain spacing and depth of either 40 m and 1-1.25 m, or 30 m and 1 m confirmed the recommended basic guidelines for Indian subsurface drainage design with optimum drainage coefficient of 2 mm.day-1 for semi-arid regions and drain spacing between 30-50 m and 1.2 m depth for fine-textured soils.

Evaluating Effect of Subsurface Drain Spacing and Depth on Hydrological Properties of Waterlogged Vertisols in Sangli, Maharashtra

A field experiment was conducted to evaluate the effect of subsurface drain spacing and depth on hydrological properties of waterlogged Vertisols under sugarcane in Sangli district of Maharashtra during 2012-13 to 2013-14. A total of 12 treatments consisting four drain spacings of 10, 20, 30 and 40 m and three drain depths of 0.75, 1.0 and 1.25 m were laid in experimental plot. The saturated hydraulic conductivity of soil was determined before and after harvesting of sugarcane. Drainable porosity of soil corresponding to water table depth was determined from water table drawdown and drain discharge measurements after rainfall. It was found that the closely-spaced and deep drain recorded better hydrological properties of soil (drainage coefficient, water table depth, saturated hydraulic conductivity, and drainable porosity) as compared to widely-spaced and deep drains. But closely-spaced drains increased the initial adoption cost of subsurface drainage system, drained excess water, and leached more nutrients. Drain spacing and depth of either 40 m and 1-1.25 m, or 30 m and 1 m confirmed the recommended basic guidelines for Indian subsurface drainage design with optimum drainage coefficient of 2 mm.day-1 for semi-arid regions and drain spacing between 30-50 m and 1.2 m depth for fine-textured soils.

Theoretical analysis and experimental verification of the improved subsurface drainage discharge with ponded water

The improved subsurface drainage is a new drainage technique which has large discharge verified by experiments. It can be used to solve the problems of frequent floods and cultivated land shortage in South China. Considering large-scale applications, a general drainage formula of the improved subsurface drainage with ponded water in a homogeneous and isotropic soil was proposed based on Kirkham equation. Firstly, the drainage formulas based on different assumptions were deduced and verified by laboratory experiment and field test. Additionally, further validation and simplification were studied by numerical simulation in which the critical conditions to distinguish whether the filter was saturated or not were given. Results showed that the proposed formulas passed the validation by laboratory experiment and field test based on Method 1 and Method 2 in which the bottom of the simplified boundary overlapped with the bottom of the drain pipe and the center of simplified boundary located at the center of filter were assumed respectively. The numerical simulation results showed the formula based on Method 1 was more applicable than that based on Method 2. Moreover, for Method 1, that (b0+h0)/d equaled 0.6 could be regarded as the critical boundary between filter saturated and unsaturated working condition. Considering the ratio of drain distance and impermeable layer depth, a more simplified formula was given. In this simplified formula, that drain spacing was three times of impermeable layer depth was a critical condition. The research results could provide scientific basis for improved subsurface drainage design and lay a good foundation for its application. Meanwhile, it would be beneficial to enrich agricultural drainage technologies and promote development of agricultural drainage in China.

Field and numerical experiment of an improved subsurface drainage system in Huaibei plain

New requirements are put forward for agricultural drainage system due to frequent floods and cultivated land shortage in Huaibei plain, China. The improved subsurface drainage is a more efficient drainage system by laying high permeability materials as filter above the drains based on conventional subsurface drainage whose function is limited by soil hydraulic conductivity. Field experiments was used to evaluate the performance of the improved subsurface drainage preliminarily and numerical experiments was used to explore the capacity of the improved subsurface drainage deeply. Based on calibration and validation by field experiment data, HYDRUS model was used to evaluate the impacts of design parameters of filter hydraulic conductivity, filter width and height, drain spacing and depth on improved subsurface drainage discharge with constant ponding depth. Then, water table depths at different distances from the pipe drain for improved and conventional subsurface drainage were simulated under initial conditions of saturated soil and no surface ponding. Besides, the daily water balance under improved subsurface drainage had been also studied. The result of field experiment showed that the discharge of improved subsurface drainage was about 1.9 times of the conventional subsurface drainage discharge under conditions of same surface ponding depths. The results of numerical experiments indicated that the improved subsurface drainage had a real-time drainage function for the reason that cumulative outflow increased by about 87% than conventional subsurface drainage within 12h after beginning draining. The improved subsurface drainage lowered water table to an appropriate depth faster than conventional ones, which could provide a more favourable soil moisture condition for crop growth. Furthermore, through daily water balance analysis of improved and conventional subsurface drainage with different rainfalls and initial water table depths, the results showed that subsurface drainage could reduce surface runoff effectively, especially for improved subsurface drainage. Good drainability of the improved subsurface drainage was beneficial to decrease the amount of soil water storage after rainfall and helpful to shorten subsequent draining time of water table drawdown. The research results could provide scientific basis for improved subsurface drainage design and lay a good foundation for its application. Meanwhile, it would be beneficial to enrich agricultural drainage technologies and promote development of agricultural drainage in China.

A diagnosis of sub-surface water table dynamics in low hydraulic conductivity soils in the sugar cane fields of Pongola, South Africa

Water and land are the two natural resources restraining crop production in South Africa. With the increasing demand for food, emphasis has shifted from the sole reliance on rain fed crop production, to irrigation. The deterioration in irrigation water quality from surface water sources is, however, posing a big challenge to the sustainability of irrigated crop production. This is because more water is required for leaching, resulting in shallow water tables in agricultural lands. The installation of well designed subsurface drainage systems alone is not enough; the provision of timely maintenance is also necessary. In this study, the extent and severity of problems as a consequence of shallow water tables and their possible causes were investigated at three sugarcane fields in Pongola, South Africa, having low hydraulic conductivity soils. Also investigated were soil salinity levels and the temporal variation in the salinity of the irrigation water. A water table map of a 32 ha sugarcane field was generated, using observed water table depth (WTD) data from 36 piezometers monitored from September 2011 to February 2012. Out of the total 32 ha under cultivation, 12% was found to be affected by shallow WTDs of less than the 1.0 m design WTD. The inability of natural drainage to cope with subsurface drainage needs and the poor maintenance of subsurface drainage systems contributed to the shallow water tables in the area. Furthermore, the currently adopted drainage design criteria also proved unsatisfactory with mean observed water table depth and drainage discharge (DD) of 20% and 50%, respectively, less than their respective design levels. The salinity of the irrigation water was, on average, 32% higher than threshold tolerance level of sugarcane. The root zone soil salinity levels at the three study sites were greater than the 1.7 dS m−1 threshold for sugar cane. The subsurface drainage design criteria adopted at the site needs to be revisited by ensuring that the slope of the land is taken into consideration in the drainage design in addition to adhering to a recommended maintenance schedule.

Modelling mid-span water table depth and drainage discharge dynamics using DRAINMOD 6.1 in a sugarcane field in Pongola, South Africa

Determining optimal subsurface drainage design parameters through monitoring of water table depth (WTD) and drainage discharge (DD) at various combinations of drain depth and spacing is expensive, both in terms of time and money. Thus, drainage design simulation models provide for a simplistic and cost-effective method of determining the most appropriate subsurface drainage design parameters. In this study, the performance of the DRAINMOD model (Version 6.1) in predicting WTDs and DDs was investigated for a 32 ha sugarcane field in Pongola, South Africa. Water table depths were monitored in 1.7 m deep piezometers installed mid-way between two drains by using an electronic dip meter with a beeper, while DDs were measured at drain lateral outlet points, using a bucket and a stop watch. Both WTDs and DDs were monitored from September 2011 to February 2012. Results of the DRAINMOD model evaluation in predicting WTD, during calibration period, showed that there was a very strong agreement between simulated and observed WTDs with a goodness-of-fit (R2) of 0.826 and a mean absolute error (MAE) of 5.3 cm. Similarly, simulated and observed DDs during the model validation period also showed very strong agreement, with an R2 value of 0.801 and an MAE of 0.2 mm∙day-1. Results of simulated WTDs at various combinations of drain depth and spacing indicated that in clay soil a WTD of 1.0 to 1.5 m from the soil surface can be achieved by installing drain pipes at drain spacing ranging from 25 to 40 m and drain depth between 1.4 and 1.8 m. On the other hand, in clay-loam soil, the same 1.0 to 1.5 m WTD can be achieved when the drain pipes are installed at drain depths ranging from 1.4 to 1.8 m and corresponding drain spacing ranging from 55 to 70 m. Based on these results, it was concluded that DRAINMOD 6.1 can reliably be used as a subsurface drainage design tool in the Pongola region. This would simplify the design of subsurface drainage systems and the formulation of subsurface drainage design criteria for different crops and soil types found in the area and possibly throughout South Africa.Keywords: drain depth; drain spacing; Hooghoudt’s equation; model performance; saturated hydraulic conductivity; steady state conditions

Climate change and subsurface drainage design: results from a small field-scale catchment in south-western Norway

Measurements on groundwater level and subsurface drain discharge have been carried in a small field-scale catchment from November 2012 to February 2013 in south-western Norway. The main objective of the measurements has been to study the interaction between the subsurface drainage discharge and groundwater level. Different methods were used to analyse the measurements. One method was to study the variation in groundwater level and drain discharge. The measurements showed there were large day to day variations. However, in addition, there were large diurnal variations in both the groundwater level and drain discharge. Also the recession of groundwater level was studied using a two-exponential decay function. During several months the precipitation largely exceeded the long-term precipitation. The measurements showed that drainage system had the capacity to react fast to precipitation-induced rise in groundwater level, resulting in a fast drawdown. The measurements at the small scale field catchment showed that the drainage system is designed and capable to react to high precipitation amounts like those predicted by climate change scenario studies.

Developing optimum subsurface drainage design procedures

The DRAINMOD simulation model was used to investigate combinations of drain depth and spacing for major soils of southern Minnesota to maximize profitability and minimize drained volume and surface runoff. Six soil types (Canisteo, Harps, Nicollet, Normania, Okoboji, and Webster) and three locations (Lamberton, Waseca, and Willmar) were included in the original study and one soil-location combination was reported on, herein (Webster–Waseca). Four drain depths (90, 105, 120, and 135 cm) were used and drain spacings were selected to simulate drainage coefficients from 3.2 to 19 mm/day. Soil input files for DRAINMOD were created using a combination of measured data from field sampling (soil texture and bulk density), data estimated with the Rosetta soil parameter model/van Genuchten equation (water retention curves), and publicly available data (soil permeability). Long-term simulations were conducted for each location using 90 years of historical climate data (1915–2005). Outputs from DRAINMOD were used to create “performance” indices that enable the concurrent consideration of profitability, drainage volumes, and surface runoff, when choosing drain depth and spacing. A spreadsheet design tool was developed to compute and display these indices, based on a few simple user inputs to define cost and crop price. Internal rate of return was used as the basis for profitability considerations. Results obtained indicated that in general, profitability may be increased with increased drain depth and spacing, due to system costs associated with narrower drain spacings. It was found that when considering both profitability and drainage volume, deeper, more widely spaced drainage systems were generally preferable, because of increased profitability and decreased drainage volumes.

Design of a New Prefabricated Road Subsurface Drainage System

Water flow through road structures is a topic of great interest in civil engineering, as water is one of the factors that most affects the hydraulic and mechanical behavior of road materials. Efficient design of subsurface drainage improves the performance of road pavement. Conventional drainage systems, such as trench drains may not be wholly effective in reducing water-related problems, and in fact, may inadvertently reduce pavement performance and service life. This can be because conventional drainage is projected in saturated conditions; however, most water flow near the surface occurs under unsaturated conditions. This paper presents an experimental study to design a new prefabricated prototype for the subsurface drainage of road pavements (SubDrain). SubDrain has been designed by using rapid prototyping Selective Laser Sintering (SLS) with powder polyamide material and experimental validation tests, with the aim to evaluate the mechanical and hydraulic behavior of the prototype. The results of this study show that the new prefabricated prototype is a potential technology solution to replace the conventional trench drain systems currently used in road projects. Findings in this study are limited to a prototype tested only under laboratory conditions.

Evaluation of Subsurface Drainage Design Based on Projection Pursuit

Soil salinization is a type of soil degradation, which is one of the biggist problems in protected agriculture. A welldesigned subsurface drainage system with reasonable drain space and depth contributes to large ratio of desalination and high crop yield. For selecting the optimization design, it is important to find out how the subsurface drainage systems affect the soil conditions and improve the harvest. In this experiment, the drainage pipes were arranged by two different patterns, the dynamics of surface soil EC was measured by salinity sensors, and the tomato yield was calculated. In order to comprehensively evaluate the rationality of subsurface drainage system, a PP(projection pursuit) model was also established. The results showed that the monthly variation of subsurface soil EC was in a trend of decline in general, drainage treatment Tr1 and Tr2 performed much better than non-drainage treatment CK. Based on the model's calculations, drain spacing 8m and drain depth 0.7m(Tr2) was selected as the preferable subsurface drainage parameter. The desalination ratio of Tr2 was 9.59% larger than CK, and 1.7% larger than Tr1; tomato yield of Tr2 reached 38796.5kg/hm2, which was 31889.9kg/hm2 higher than CK, and 6823kg/hm2 higher than Tr1.

Modeling the impact of alternative drainage practices in the northern Corn-belt with DRAINMOD-NII

The hydrologic and water quality impacts of subsurface drainage design and management practices are being investigated through field and simulation studies throughout the northern Corn-belt. Six years of data from an ongoing field study in south central Minnesota ( Sands et al., 2008 ) were used to support a modeling effort with DRAINMOD-NII to investigate: (1) the performance of the model in a region where soils are subject to seasonal freeze–thaw and (2) the long-term hydrologic and water quality characteristics of conventional and alternative subsurface drainage practices. Post-calibration model prediction and efficiency were deemed satisfactory using standard model performance criteria. Prediction errors were primarily associated with early spring snowmelt hydrology and were attributed to the methods used for simulating snow accumulation and melting processes, in addition to potential sublimation effects on ET estimates. Long-term simulations with DRAINMOD-NII indicated that drainage design and/or management practices proposed as alternatives to conventional design may offer opportunities to reduce nitrate (NO 3 )-nitrogen losses without significantly decreasing (and in some cases, increasing) crop yields for a Webster silty clay loam soil at Waseca, Minnesota. The simulation study indicated that both shallow drainage and controlled drainage may reduce annual drainage discharge and NO 3 -nitrogen losses by 20–30%, while impacting crop yields from −3% (yield decrease) to 2%, depending on lateral drain spacing. The practice of increasing drainage intensity (decreasing drain spacing) beyond recommended values appears to not significantly affect crop yield but may substantially increase drainage discharge and nitrate-nitrogen losses to surface waters.